This invention pertains to drain closures and, more particularly, to drain closures of the type used in connection with accumulators.
There are various types of accumulators. One common type of accumulator has a rigid container with a flexible and expansible bladder therein. The bladder may be filled with a compressible fluid, such as a gas. Air or any inert gas may be used. The bladder is usually pressurized through approximately one half the total system pressure.
Outside the bladder, and within the rigid accumulator chamber, a substance is stored which is, relative to the gas, non-compressible. This substance, which is often an oil or another liquid used in hydraulics, is stored within the accumulator at a higher pressure. As such, the compressible gas may be compressed by the relatively non-compressible oil until the pressures in the accumulator are equalized. Upon the demand of the system to which the accumulator is attached, the stored energy in the bladder will force the stored non-compressible oil through the accumulator drain until, ideally, all the oil has been expelled from the accumulator. Thus, energy stored within the compressed bladder causes the bladder to expand until it completely fills the chamber. The expanding bladder depresses a drain closure. Unless the drain closure remains open until substantially all of the stored oil in the accumulator is expelled, some of the oil will be trapped and not be available for useful purposes within the system to which the accumulator is attached. In addition, where the bladder, upon expanding, extrudes past the drain closure, it is likely to become pinched or torn and eventually fail, thereby making the accumulator inoperative. This is a substantial problem and one which has plagued the operation of prior art accumulators.
To retain the drain closure open so that substantially all of the stored oil may be expelled from the accumulator, a relatively strong spring is used to bias open the valve closure. However, the spring cannot be so strong as to keep the closure open so that the bladder extrudes past the drain closure head, with the above-indicated resulting injury.
If, on the other hand, a relatively weak spring is used to insure that the drain closure closes before the bladder can be extruded, the force of the bladder immediately overcomes the force of the spring and closes the drain closure while the accumulator is still charged with a considerable quantity of the stored oil. Furthermore, in the event a large rate of flow of the stored oil is required during any short period of time, such as, for example, in the operation of a hydraulic brake, the flow of such fluid would result in a low pressure area beneath the drain closure and a high pressure area within the accumulator chamber. As a result, a relatively weak spring would not be able to overcome the differential pressure on both sides of the closure head and the latter may close almost immediately after the flow of the stored oil begins.
There have been a number of approaches to providing an efficient drain closure. Thus, Mercier, in U.S. Pat. No. 2,932,320, provides a valve in which a generally cylindrical drain has a hollow piston slidable secured therein. A leaf spring is within the drain housing and bears against the side walls thereof, and is secured within the piston centrally to the piston top. Circular holes are in the cylindrical side walls of the hollow piston to permit the stored oil to enter and leave the accumulator chamber through the drain. The valve member provided by Mercier is characterized by having a lip which overhangs the accumulator port, so as to seal the drain shut.
Mercier, in U.S. Pat. No. Re. 23,333, proposes another valve construction for an accumulator, in which the hollow piston is centrally supported by a coil spring. As with the device first proposed by Mercier U.S. Pat. No. 2,932,320), substances entering or leaving the accumulator chamber will pass directly about the spring. Like that first Mercier device, the apertures in the side of the piston are generally circular in configuration and extend radially with respect to the cylindrical piston.
Berger, in U.S. Pat. No. 2,659,391, suggests a hollow cylindrical valve stem in a drain valve. The valve stem portion of the valve head has an overhanging lip which engages and seals shut the accumulator drain port. The spring in this instance is a cylindrical spring coiled about the outside of the valve stem and bears against the overhanging lip.
Still another device is offered by EMG Hydraulics, Inc. of Santa Monica, California, in which a poppet valve is disclosed. A solid valve stem supports a valve head which is chamferred so as to fit into registry with the accumulator port inside the accumulator housing. A coiled spring is about the stem of the poppet and resiliently pushes the head upwardly.
Most of the aforementioned devices have a common misinterpretation of the purpose of the accumulator drain closure. In each instance, the devices proposed are valves and the valve closures proposed are intended to seal shut the opening once the bladder has pressed the closure shut. Because of the emphasis upon tight sealing, the overhanging lip of the devices proposed by Berger and Mercier (U.S. Pat. No. 2,932,320), as well as the engaging edges of the EMG Hydraulics, Inc. device, tend to catch or engage the bladder and damage it. All the devices have in common the fact that the spring used to urge the closure into an open position are directly in the flow of the stored material. It is believed that the impingement of such material upon the spring will have a detrimental effect. It may vary the spring's resiliency in response to the flow-rate, direction of flow, and viscosity of the stored substance.
In the discussed devices, the springs bear against the underside of the closure top because the center support provided by the spring (e.g. Mercier in U.S. Pat. No. Re. 23,333), the diametral clearance between the housing and valve must be snug in order to avoid having the valve pivot in the housing and scar the housing wall. This requirement further blocks the flow of stored substances from the accumulator once the port is closed by the valve.
The valve drain holes in hollow valves tend to be small and circular. Liquids flowing from the accumulator chamber and into the drain are required to change direction sharply thereby reducing pressure in the valve. The increased pressure differential between the valve and the accumulator may cause premature closing of the valve. A similar defect may be seen in the EMG device in which a member is inserted in the drain for supporting the centrally located spring and poppet valve. The liquid flow area is sharply constricted to thereby increase the pressure differential.
Prior art closure valve-type devices have proven to be inefficient, tending to prematurely close and entrapping the stored medium and, in some designs, capturing and damaging the bladder.